diff --git a/src/erc7730/convert/calldata/v1/enum.py b/src/erc7730/convert/calldata/v1/enum.py
index 3b1bfe84..3d78f6ab 100644
--- a/src/erc7730/convert/calldata/v1/enum.py
+++ b/src/erc7730/convert/calldata/v1/enum.py
@@ -9,6 +9,26 @@
 from erc7730.model.resolved.context import ResolvedDeployment
 from erc7730.model.types import Id, Selector
 
+# A bool holds 0 or 1 in calldata, and an enum key is the field value it matches, so these are
+# the keys a descriptor writes for a bool field. JSON has no bool object key, so they arrive as
+# text, and the casing follows whoever wrote the descriptor rather than any rule.
+BOOLEAN_ORDINALS = {"true": 1, "false": 0}
+
+
+def enum_ordinal(ordinal: str) -> int:
+    """Value the device compares an enum entry against.
+
+    :param ordinal: enum key, as written in the descriptor
+    :return: the numeric field value it stands for
+    :raises ValueError: if the key is neither decimal nor a boolean literal
+    """
+    try:
+        return int(ordinal)
+    except ValueError:
+        if (value := BOOLEAN_ORDINALS.get(ordinal.strip().lower())) is not None:
+            return value
+        raise
+
 
 def convert_enums(
     deployment: ResolvedDeployment, selector: Selector, enums: dict[Id, EnumDefinition] | None
@@ -29,7 +49,7 @@ def convert_enums(
             selector=selector,
             id=i,
             enum_id=enum_id,
-            value=int(ordinal),
+            value=enum_ordinal(ordinal),
             name=name,
         )
         for i, (enum_id, enum) in enumerate(enums.items())
diff --git a/tests/convert/calldata/v1/test_enum_ordinal.py b/tests/convert/calldata/v1/test_enum_ordinal.py
new file mode 100644
index 00000000..ef830a04
--- /dev/null
+++ b/tests/convert/calldata/v1/test_enum_ordinal.py
@@ -0,0 +1,40 @@
+import pytest
+
+from erc7730.convert.calldata.v1.enum import enum_ordinal
+
+
+@pytest.mark.parametrize(
+    "ordinal,expected",
+    [
+        pytest.param("0", 0, id="zero"),
+        pytest.param("1", 1, id="one"),
+        pytest.param("42", 42, id="larger"),
+        pytest.param("-1", -1, id="negative"),
+    ],
+)
+def test_a_decimal_key_is_its_own_value(ordinal: str, expected: int) -> None:
+    assert enum_ordinal(ordinal) == expected
+
+
+@pytest.mark.parametrize(
+    "ordinal,expected",
+    [
+        pytest.param("false", 0, id="false"),
+        pytest.param("true", 1, id="true"),
+        pytest.param("False", 0, id="False"),
+        pytest.param("True", 1, id="True"),
+        pytest.param("FALSE", 0, id="FALSE"),
+        pytest.param("TRUE", 1, id="TRUE"),
+        pytest.param(" true ", 1, id="padded"),
+    ],
+)
+def test_a_boolean_key_is_the_value_the_bool_holds_in_calldata(ordinal: str, expected: int) -> None:
+    """A bool holds 0 or 1, and the casing follows whoever wrote the descriptor."""
+    assert enum_ordinal(ordinal) == expected
+
+
+@pytest.mark.parametrize("ordinal", ["maybe", "", "0x1", "1.0", "yes"])
+def test_a_key_that_is_neither_still_raises(ordinal: str) -> None:
+    """Silently mapping an unrecognised key to a number would build an entry that never matches."""
+    with pytest.raises(ValueError):
+        enum_ordinal(ordinal)